constellation/image/measured-boot/precalculate_pcr_4.sh

#!/usr/bin/env bash
# Copyright (c) Edgeless Systems GmbH
#
# SPDX-License-Identifier: AGPL-3.0-only

# This script is used to precalculate the PCR[4] value for a Constellation OS image.
# Usage: precalculate_pcr_4.sh <path to image> <path to output file>

set -euo pipefail
shopt -s inherit_errexit
source "$(dirname "$0")/measure_util.sh"

ev_efi_action_sha256=3d6772b4f84ed47595d72a2c4c5ffd15f5bb72c7507fe26f2aaee2c69d5633ba
ev_efi_separator_sha256=df3f619804a92fdb4057192dc43dd748ea778adc52bc498ce80524c014b81119

authentihash () {
    local path="$1"
    "$(dirname "$0")/extract_authentihash.py" "${path}"
}

write_output () {
    local out="$1"
    cat > "${out}" <<EOF
{
    "pcr4": "${expected_pcr_4}",
    "efistages": [
        {
            "name": "shim",
            "sha256": "${shim_authentihash}"
        },
        {
            "name": "systemd-boot",
            "sha256": "${sd_boot_authentihash}"
        },
        {
            "name": "uki",
            "sha256": "${uki_authentihash}"
        }
    ]
}
EOF
}

DIR=$(mktempdir)
trap 'cleanup "${DIR}"' EXIT

extract "$1" "/efi/EFI/BOOT/BOOTX64.EFI" "${DIR}/01-shim.efi"
extract "$1" "/efi/EFI/BOOT/grubx64.efi" "${DIR}/02-sd-boot.efi"
extract "$1" "/efi/EFI/Linux" "${DIR}/uki"
sudo chown -R "${USER}:${USER}" "${DIR}/uki"
cp "${DIR}"/uki/*.efi "${DIR}/03-uki.efi"

shim_authentihash=$(authentihash "${DIR}/01-shim.efi")
sd_boot_authentihash=$(authentihash "${DIR}/02-sd-boot.efi")
uki_authentihash=$(authentihash "${DIR}/03-uki.efi")
cleanup "${DIR}"

expected_pcr_4=0000000000000000000000000000000000000000000000000000000000000000
expected_pcr_4=$(pcr_extend "${expected_pcr_4}" "${ev_efi_action_sha256}" "sha256sum")
expected_pcr_4=$(pcr_extend "${expected_pcr_4}" "${ev_efi_separator_sha256}" "sha256sum")
expected_pcr_4=$(pcr_extend "${expected_pcr_4}" "${shim_authentihash}" "sha256sum")
expected_pcr_4=$(pcr_extend "${expected_pcr_4}" "${sd_boot_authentihash}" "sha256sum")
expected_pcr_4=$(pcr_extend "${expected_pcr_4}" "${uki_authentihash}" "sha256sum")

echo "Authentihashes:"
echo "Stage 1 – shim:                       ${shim_authentihash}"
echo "Stage 2 – sd-boot:                    ${sd_boot_authentihash}"
echo "Stage 3 – Unified Kernel Image (UKI): ${uki_authentihash}"
echo ""
echo "Expected PCR[4]:                      ${expected_pcr_4}"
echo ""

write_output "$2"